HE general unsettling of human relations which came as a consequence of the World War raised wide questioning as to the future of civilization and the ultimate fate of mankind. Evidences of disintegration in so much that had appeared fixed in social organization naturally caused us to review the guarantees of orderliness and progress to which we had been accustomed. In consideration of such questions we have naturally come to inquire as to the expectation of continuity in the process of creation, so marvellously expressed in the history of the world up to this time.

Many practical persons assume that no special reason exists for concern with anything that moves so slowly that it does not make itself felt in a measurable way in the special interests of a single generation. But we must remember that society is a continuing thing, not limited by generations. It is interested in its own future, and whatever touches this concerns also the immediate personal relations of all individuals involved. There is certain to be wide difference between the psychology of persons in a world expecting progress and one anticipating stagnation or decay. This will be true regardless of immediacy of either progress or disintegration.

There is nothing contributing to the support of our lives in a spiritual sense that seems so clearly indispensable as that which makes us look forward to continuing growth or improvement. It is difficult to believe that human life could exist without such expectation. Whatever concerns the basis of this belief is vital.

Nearly every people with a history sufficiently long to permit accumulation of

results from mature thinking has set down some form of expression of its views concerning the meaning of its own creation. In a great percentage of these statements the central thought is mainly that we have not always existed, and must therefore have been brought into being by forces beyond human control. It is not improbable that in certain of these stories, as in those of India and Egypt, there is more than a mere statement of the fact that we were created. There are not only suggestions as to the steps by which our environment was prepared, but stages in the development of man himself seem to have been considered.

With advance in interpretation of nature by modern philosophic science, we have come to learn an extraordinary story of the history of our earth and its inhabitants. While science has not attempted an explanation of ultimate origins, it has gone far to show how nature and man developed to their present state.

The astronomer and geologist have left us no room for doubt regarding the vast extent of time in which the world has existed; the geologist has given us a movingpicture of our earth through a long series of stages preceding that in which we know it to-day; the paleontologist has made us acquainted with innumerable changes in life of the earth leading up to appearance of man and then on to the present. The biologist has come to understand something of processes by which life produces life, and of principles which control production not merely of new individuals but of new kinds of living things as well.

As I see the meaning of these advances, the great contribution through science is not merely in the fact that we learn of our having been created-we knew that already-nor in the idea that we have a history, as everybody suspected that also

-nor yet in the evidence that we have come into being through a long series of stages of growth which had not been known to us. Rather does the value of scientific contribution, in the historical sense, reside in the evidence which it furnishes that the movement shown in nature through vast ages makes known in some measure the character of the thing with which we deal. Science expresses the idea of unity in nature and its laws, and continuity in their operation. It indicates that what we see does not merely concern man and the present day, but is something larger than present or past alone.

The greater part of the history of our earth is a matter for consideration of the astronomer. Geology deals only with its most recent events. In its relation to the extended reaches of astronomy, geological history shrinks to a relatively minute stretch in the field of time.

By the method of measurement now used it has been shown that our solar system is a mere speck in that great assemblage of stars which we call the Milky Way. We begin to form a conception of the size of this realm when we realize that it takes light, travelling at the rate of one hundred and eighty-six thousand miles per second, a time estimated at more than one hundred thousand years, to cross this star field.

But the astronomer does not permit us to rest with these figures as finality in measurement of space or time. The Milky Way in which we live is a unit field of stars hanging in space, and there are other bodies which resemble it in the region outside this star system. The spiral nebulæ, among the most beautiful objects of the heavens, lie beyond the limits of our special universe. Many of these nebulæ seem to represent other universes, comparable to our Milky Way. Perhaps they attain dimensions even greater than in our system, but are so far removed that only the light-gathering power of a great telescope makes them visible. The distance of such bodies may be almost beyond our power to appreciate. The elements of time involved in this story, as we read it, are beyond adequate expression, but this question of time and space has its intimate bearing upon the prob

lem of the continuity of conditions which make life possible upon this earth.

The record of the rocks, from which we read geological history, does not cover more than a small portion of the past of this planet. We find that the most ancient strata observed are, by reason of their great age, broken, shattered, and changed into new mineral combinations by pressure, heat, and other forces. These oldest known rocks rest upon a basement which was once molten material that has come into its present position since the rocks now above it were formed. The oldest strata thus far examined rested once upon a foundation which represented a still earlier time. That basement is now destroyed or replaced by melted rocks of later date. It thus appears that we have lost the beginnings of our geological record, and there is reason to believe that what is lost may represent a period as long as that covered by all of the strata that remain.

What we have left of the record is not, however, an unimportant story. The strata available when carefully pieced together give a total thickness of more than fifty miles. Calculated by various methods, the more conservative estimates of the time required for accumulation of this pile are now measured in hundreds of millions of years, with the tendency of leading geologists toward lengthening the time to cover at least one thousand million years.

There is much evidence in the rocks indicating the conditions of atmosphere and temperature under which the successive strata of the geological record were deposited. It has been possible to form a fairly clear picture of the many climatic variations to which the earth has been subjected within the range of our available record. At one time it was believed that the climate of early geological periods was relatively very warm, and that as ages passed the earth cooled down to a condition illustrated by the glacial epoch immediately preceding the present geological stage.

The most recent studies have shown that in the known period of earth history there is no evidence of very great change in climatic conditions of the earth as a whole. There are records of many glacial

periods, some even in the earlier ages. There have been many minor changes from warm to cool periods, and the reverse; but, in general, the physical conditions obtaining on the earth one hundred million or more years ago were not materially different from those on the world, as a whole, to-day. This statement should not be interpreted to mean that minor changes of climate have not taken place within this vast period. There have been almost continuous climatic fluctuations, but the extreme range has been within very narrow limits. So closely has the range been restricted that in terms of the changes expressed in the physical evolution of a star or a planet the difference between climate of the earliest geological stages we know on the earth and that of the present is almost negligible. This means that in terms of evolution of heavenly bodies, the vast geological history of the earth now open for our inspection is probably only a brief span compared with the preceding astronomical and geological ages of which we have no record—and that, judging by history as we know it, there is no reason why conditions like those which have obtained here for long ages should not continue, without material alteration, for a further period comparable to the time of which we have knowledge.

It was for a long time customary in physics and in astronomy to look upon our solar system as a mechanism of the type of a clock rapidly running down. The sun has been assumed to be growing cold. Inasmuch as the earth is dependent for its heat upon the sun, many have looked forward to a dead earth, the disappearance of life, extinction of man, and many other natural consequences following in the train of this physical change. Recently, however, it has been shown that the life period of the sun may be enormously lengthened by the breaking down of matter into radiant energy. This, it is held, will lengthen the life of the sun many thousand times, and by this change there is opened the possibility of the extension of conditions of temperature which govern life upon the earth for a period of vast

extent.

Knowing that present conditions of atmosphere and temperature reach back to earliest known geological records, it is

not surprising that with continuing search the paleontologist and geologist have found evidences of varied life in earlier and still earlier strata, until there are now known in the older groups of rocks sufficiently well-preserved traces to tell us of living things which existed in that early time.

Many of the most ancient rocks have been so crushed or otherwise altered that they have lost their original character entirely. Such strata could not be expected to contain remains of animals or plants, even if they were entombed in them at the time these rocks were forming as layers of mud, sand, gravel, or other deposits accumulating naturally in ancient seas, lakes, and rivers.

Remains of life from the older rocks are not limited to the simplest forms found on the earth, but are of many kinds. If the evolution theory presents a true picture of history of life, the earliest types should be the simplest stage, from which the more complicated forms would later be developed. It has been assumed by some that as this ancient life is fairly advanced and differentiated it furnishes definite evidence contradictory to the theory of evolution; but when we remember that the earlier part of our geological record is absent because it was destroyed, we recognize the earliest known stages of life as just what we should expect to find under known conditions.

We do not know when life appeared upon earth. Presumption favors the view that we shall never find the portion of the geological record which might contain this evidence. If existence of life on this planet is governed by presence of physical conditions, in a general way comparable to those which now obtain, living things may have been present here in time preceding our first record, for a period as long as or longer than the entire space of known geological history.

Just as we realize that while our total geological record is only a part of what might be known, but is none the less a vastly long period measured in terms of human history, we should understand that, though we do not see the beginning of life history, the record now open to us is actually of great extent and tells much of the nature and movement of life.

Somewhat in the manner in which physical conditions on the earth show continuous variation, so our record indicates that life changed continually through geological time. Each stage of the geological record is characterized by remains of animals and plants similar to and yet mainly differing from those of immediately preceding and following ages. While fluctuation in physical conditions between the beginning and end of the record available has not resulted in marked deviation from an original standard, we find that in history of life the changes are in general cumulative modifications in definite directions. The fossil remains found in rocks of each stage of the record are not merely different from those representing life of other periods, but they form series in which the representatives from earlier time are generally of less complicated structure. In terms of the nervous system, the older forms were less intelligent.

The facts of occurrence or succession of remains of living forms indicate that they are in the order in which they would appear if the life represented in the strata formed in each successive period were descended from that of the preceding period, but had been modified away from its parent stock in the process of descent. Thus we have the suggestion that the whole succession is connected through blood relationship.

This trend of movement or of growth we see operating continuously from the time life appears in the geological record up to the present. The movement comes to be recognized so clearly as a habit of nature that we are surprised, and seek for explanation if an apparent exception appears.

The question as to what made organisms pass through this long series of changes represented in the geological record must be answered by the biologist; as also the inquiry as to how these modifications are related to variation in physical conditions of the earth which has formed their environment during this period of change. Biology has made great advance in those studies of variation in characters of living types of animals and plants which will be necessary in approaching the solution of these problems. We know, first of

all, that we must account for the origin of individuals and of races of living things by their development out of preceding or ancestral types. While there may be foundation for belief in the generation of the simplest forms of biological mechanism from things which seem to be nonliving, there is no ground for belief in the origin of any higher form of life except by birth from other life.

Development of the individual has been the subject of exhaustive study covering processes of reproduction and growth, until we begin now to understand the meaning of change from one generation to the next. The problem of how a new kind or variety or species of life comes to be derived from another we find involved in study of the mechanism by which individuals originate, and also the manner in which the individual relates itself to its environment. One group of biologists holds that in the origin of new forms the major emphasis is to be placed upon the mechanism of inheritance; another that environmental influence is the factor of major importance. Others consider that each of these factors is important; heredity being the gravitational element which holds nature steady; environment, through a wide range of complicated relations, tending to make the individual and its descendants accommodate themselves to the shift of their surroundings.

Regardless of the particular theory used in explanation, there is reason to believe that the influences governing known development of life through the ages are related in part to variation in physical conditions at the same time in different places. Moreover, we know that the crust of the earth has been in almost constant movement through geological time. Mountains have grown up and been worn down. Great land areas were lowered and became groups of islands, or have disappeared entirely beneath the sea. other points uplift of the crust raised the sea-floor and formed land. These fluctuations in the position of the earth's crust, together with the influence of changes in climate, have forced life into almost constant adjustment, either to new conditions in the same place, or to similar conditions in different places, and have thus been either the cause or occasion of continuing

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new forms of life.

His course of history follows laws of dis

From stage to stage, through a period

tinues.

Let us now recall that vast as the period seems during which life has existed on the earth it may be only a fragment of history geologically, and is presumably a mere moment measured in our astronomical history. We note that variation of physical conditions during this period has been within extremely narrow limits. Unless some new element is introduced to influence earth history, what we now know of factors governing the life period of the sun, which is the source of heat and light on the earth, makes it difficult for us to imagine conditions changing so radically as to prevent existence of life on the earth for a long period to come. Given continuity of present conditions we should assume that variation and evolution or forward movement will go on for yet a very long time.

This growth or movement of life is characterized at the same time by instability and by progress. It is a process of creation, in that it constantly brings into being types that have not existed before. In the biological sense it is a continuing process which should proceed without interruption unless some new force is introduced to arrest it.

When we consider the place of the human group in this world of life on the earth we realize that man is not a creature of the present day alone, but that he comes out of the remote past, and his history merges into that of the cave-bear and sabre-tooth tiger. Man evidently came into being as a part of the world of living things by a process of creation which did not differ materially from that by which other organic types arose. He appeared at the moment in geological time when we would expect him if he is a product of

To-day we see man distributed over the whole earth, varying widely in physical characters in different parts of his habitat. He shows a relation of his physical differences to variation of environment in a manner similar to that exhibited by the wide range of animals and plants known so well through our studies of distribution, variation, and evolution of organisms in past periods.

At the present rate of progress it seems quite certain that within a few centuries the human race will have almost complete control of the biological world. Man will take what he wishes. He will determine what plants and animals he desires to retain, and what may be eliminated. Much of the power of nature will be harnessed and directed to his use.

When we consider the relation of future biological or creative evolution to human beings we find a number of leading students inclined to believe that further development of man will be shifted entirely from physical to so-called social evolution, involving development of institutions with accumulation and organization of knowledge. This social development is characterized by its relation to a train of continuing experience. Individuals disappear but the body of knowledge and the consciousness of society persist. In this phase of evolution discovery and research contribute by bringing in new knowledge, science and learning serve to organize information, business makes knowledge effective, education carries it from one man to another or from one generation to the next. The body of knowledge involved in the social organism may grow indefinitely. There seems almost no limit to the distance which humanity may go in increasing acquaintance of its environment, as well as in understanding the